my $storage_dir = "C:/Stuff/";
foreach my $category qw( abc def ghi ) {
  foreach my $subcategory qw( this that ){
    foreach my $year ( 1..3) {
      my $file = sprintf("%s_%s_02d.csv", $category, $subcategory,$year);
      my $path = $storage_dir.$file;
      # now do something with the file, i.e. generate your plot command
      do_plot( $path ); 
    }
  }
}

sub do_plot {
  my $path - shift;
  ### do the actual plotting here
}